PET-4, as it was called when I arrived up here would imply PET-1, PET-2, PET-3 and who knows how many other PETs. If they will need this one in time of war, though, it would have to be a tough war, because it would take a very long time to start getting the oil out.
That may have been a factor in the decision to sell or transfer them. The navy no longer steams on 'bunker fuel,' essentialy crude oil. It requires refined products.